GitHub uses what we're calling "GitHub Flavored Markdown" (GFM) for messages, issues, and comments. It differs from standard Markdown (SM) in a few significant ways and adds some additional functionality.
If you're not already familiar with Markdown, you should spend 15 minutes and go over the excellent Markdown Syntax Guide at Daring Fireball.
If you prefer to learn by example, see the following source and result:
Differences from traditional Markdown
The biggest difference that GFM introduces is in the handling of linebreaks. With SM you can hard wrap paragraphs of text and they will be combined into a single paragraph. We find this to be the cause of a huge number of unintentional formatting errors. GFM treats newlines in paragraph-like content as real line breaks, which is probably what you intended.
The next paragraph contains two phrases separated by a single newline character:
Roses are red Violets are blue
Roses are red
Violets are blue
Multiple underscores in words
It is not reasonable to italicize just part of a word, especially when you're dealing with code and names often appear with multiple underscores. Therefore, GFM ignores multiple underscores in words.
GFM will autolink standard URLs, so if you want to link to a URL (instead of setting link text), you can simply enter the URL and it will be turned into a link to that URL.
A bit of the GitHub spice
In addition to the changes in the previous section, certain references are auto-linked:
* SHA: be6a8cc1c1ecfe9489fb51e4869af15a13fc2cd2 * User@SHA ref: mojombo@be6a8cc1c1ecfe9489fb51e4869af15a13fc2cd2 * User/Project@SHA: mojombo/god@be6a8cc1c1ecfe9489fb51e4869af15a13fc2cd2 * \#Num: #1 * User/#Num: mojombo#1 * User/Project#Num: mojombo/god#1
- SHA: be6a8cc
- User@SHA ref: mojombo@be6a8cc
- User/Project@SHA: mojombo/god@be6a8cc
- #Num: #1
- User/#Num: mojombo#1
- User/Project#Num: mojombo/god#1
The newline and underscore modification code can be seen below. If you find a bug in the rendering, we'd love to hear about it.<script src="http://gist.github.com/118964.js"></script>